For example, Patent Document 1 discloses a device known as a seat slide device for a vehicle. FIG. 8 shows the seat slide device for a vehicle, which includes a lower rail 101 and an upper rail 111. The upper rail 111 is coupled to the lower rail 101 to be movable in the vehicle front-rear direction (the direction perpendicular to the sheet of FIG. 8).
The lower rail 101 is substantially uniform in cross-section in the vehicle front-rear direction. The lower rail 101 has a pair of first vertical walls 102, which extends vertically on the widthwise two sides, and a bottom wall 103, which couples the lower ends of the first vertical walls 102 to each other. A first flange 104 continuously extends from the upper end of each first vertical wall 102. The first flange 104 projects widthwise inward from the upper end of the first vertical wall 102 and is folded back toward the bottom wall 103.
The upper rail 111 is substantially uniform in cross-section in the vehicle front-rear direction. The upper rail 111 has a pair of second vertical walls 112, which extends vertically between the first flanges 104 of the lower rail 101, and a top wall 113, which couples the upper ends of the second vertical walls 112 to each other. A second flange 114 continuously extends from the lower end of each second vertical wall 112. The second flange 114 projects widthwise outward from the lower end of the second vertical wall 112 and then is folded back toward an area between the corresponding first vertical wall 102 and the corresponding first flange 104.
A first lower ball guide 105 is formed at the coupling portion between each first vertical wall 102 and the bottom wall 103, and a second lower ball guide 115 is formed at the lower end of each second flange 114. A lower ball 120a is rotationally arranged between the first lower ball guide 105 and the corresponding second lower ball guide 115. The coupling portion between the first vertical wall 102 and the corresponding first flange 104 includes a first upper ball guide 106. The second flange 114 has an upper end portion including a second upper ball guide 116. An upper ball 120b is rotationally arranged between the first and second upper ball guides 106 and 116.
The lower ball 120a and the upper ball 120b are rotational between the upper rail 111 and the lower rail 101. Thus, the lower rail 101 supports the upper rail 111 to be movable in the vehicle front-rear direction.